Approximately every 29.5 days, the moon completes one cycle called lunation.During this cycle of 29 days, 12 hours and 44 minutes, the natural satellite of the Earth goes through eight different phases.

During the first four phases of this cycle, we say that the moon is waxing.During the last four phases, it is decreasing.

- During the first quarter, the moon as a D: if one leg is added to this letter, the letter P is obtained which identifies the First Quarter

- Conversely, during the last quarter, the moon is shaped It.s C: if you add a vertical bar is obtained the letter that allows to recognize the last quarter.